This invention relates to determining the relative concentrations of oil and water phase fluids within subterranean reservoirs by measuring the chromatographic separation of tracers having distinctly different partitioning coefficients in between the oil and water phases of the fluids within the reservoirs. More particularly, the present invention relates to improving a process for making such determinations by injecting a CO.sub.2 -containing aqueous solution of reactants arranged to contain or provide a depletion of the CO.sub.2 concentration to serve as an immobile-fluid-tracer and a selectively water-miscible, radioactive mobile-fluid-tracer, in a manner such that radiation detection can be used for determining the chromatographic separation between the tracers.
A method for determining the relative amounts of water and oil fluid phases within a subterranean reservoir by injecting carrier fluid containing a reactant, such as ethyl acetate, capable of forming at least two tracers which have different partitioning coefficients between the carrier fluid and the oil phase and measuring the chromatographic separation of the tracers, was described in 1971 in U.S. Pat. Nos. 3,590,923 and 3,623,842. U.S. Pat. No. 3,751,226 by R. J. Hesse and R. F. Farmer relates to improving such a process by injecting a solution in which the traceer forming reactant is a hydrolyzable beta-keto ester such as ethylacetolacetate. U.S. Pat. No. 3,847,548 relates to improving such a process by injecting carrier fluid containing tracers which partition differently in respect to temperature changes and injecting that fluid at a temperature different from the reservoir temperature. U.S. Pat. No. 3,856,468 relates to improving such a process by injecting carrier fluid containing both a precursor which forms a tracer material that partitions between the fluid phases and a tracer material which is inert and substantially completely dissolved in the mobile phase. U.S. Pat. No. 3,990,298 relates to improving such a process by injecting a carrier fluid containing a plurality of precursors each of which forms a tracer which has a distinctive partition coefficient with at least one mobile fluid phase within the reservoir. U.S. Pat. Nos. 4,099,565 and 4,165,746 relate to uses of such a fluid saturation determining process for evaluating the effectiveness of a design process for recovering oil.
U.S. Pat. No. 4,122,896 by R. F. Scheuermann, E. A. Richardson and C. C. Templeton relates to acidizing a reservoir by injecting an aqueous solution of halocarboxylic acid salt so that the rate of the acidization is limited to the rate of its hydrolysis. The disclosures relating to hydrolysis of halocarboxylic acids contained in that patent are incorporated herein by reference.